Effect of wet reduction on catalyst stability and methods of maintaining catalyst stability

ABSTRACT

The present invention provides a method of increasing stability of a catalyst used in a dehydrogenation process. The method includes storing fresh catalyst in a reduction zone, passing a gas through the reduction zone, introducing hydrocarbons and hydrogen gas into a reactor positioned downstream from the reduction zone to facilitate a dehydrogenation reaction, and replenishing spent catalyst in the reactor with fresh catalyst from the reduction zone. The gas has a moisture content at or below about 4000 ppmv and a temperature at or below about 290° C. The reactor includes catalyst for increasing the rate of the dehydrogenation reaction. The moisture content of the gas may be reduced to at or below about 4000 ppmv by passing the gas through a drier or by using an inert gas stream. The temperature of the gas may also be reduced.

FIELD OF THE INVENTION

The present invention relates to the field of hydrocarbondehydrogenation processes. In particular, the present invention relatesto systems and methods for increasing the stability of catalysts used inhydrocarbon dehydrogenation processes.

DESCRIPTION OF RELATED ART

Platinum-based catalysts are used for numerous hydrocarbon conversionprocesses. One such hydrocarbon conversion process is thedehydrogenation of hydrocarbons, such as the conversion of long chainparaffins to olefins. The olefins can be further converted to producecomponents such as linear alkyl benzene (LAB), which can then besulfonated to produce linear alkylbenzene sulfonate (LAS). Both LAB andLAS are commonly used raw materials in the manufacture of biodegradabledetergents.

Catalyst development is directed by improvements in three areas:catalyst activity, catalyst selectivity and catalyst stability.

SUMMARY OF THE INVENTION

The present invention provides a method of increasing stability of acatalyst used in a hydrocarbon dehydrogenation process. The methodincludes storing fresh catalyst in a reduction zone, passing a gasthrough the reduction zone, introducing hydrocarbons and hydrogen gasinto a reactor positioned downstream from the reduction zone tofacilitate a dehydrogenation reaction, and replenishing spent catalystin the reactor with fresh catalyst from the reduction zone. The gas hasa moisture content at or below about 4000 ppmv. The reactor includescatalyst for increasing the rate of the dehydrogenation reaction. Themoisture content of the gas may be reduced to at or below about 4000ppmv by passing the gas through a drier or by using an inert gas stream.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a first embodiment of a hydrocarbondehydrogenation system.

FIG. 1B is a schematic view of a second embodiment of the hydrocarbondehydrogenation system.

FIG. 2 is a schematic view of a third embodiment of the hydrocarbondehydrogenation system.

FIG. 3 is a schematic view of a third embodiment of the hydrocarbondehydrogenation system.

DETAILED DESCRIPTION

FIG. 1A shows a schematic view of a first embodiment of a hydrocarbondehydrogenation system reactor section 10 with an integrated catalyststability system 12. The catalyst stability system 12 functions toincrease the life of catalysts used in the hydrocarbon dehydrogenationsystem reactor section 10 by increasing the stability of catalystshoused remotely from or integrated above the reaction zone, or from thelocation in which the dehydrogenation reaction takes place. By eithermaintaining or increasing the stability of the catalyst while beingstored, the lifetime of the catalyst also increases. Although thecatalyst stability system 12 is discussed as being used in conjunctionwith a hydrocarbon dehydrogenation process, the catalyst stabilitysystem 12 may be used in conjunction with any industrial process whereit is desired to increase the life of catalyst housed separately from orintegrated above the reaction zone.

The hydrocarbon dehydrogenation system reactor section 10 includes thecatalyst stability system 12, a recycle gas compressor 14, a reactor(which may be a reaction zone of a single stacked reactor) 16, areduction zone (of a single stacked reactor) or hopper 18, a hydrocarbonline 20, a hydrogen recycle gas line 22, a hydrogen reduction gas line24, a combined feed line 26, a reduction gas vent line 28, a catalysttransfer line 30, a reactor effluent line 32, a combined feed line heatexchanger 34, a combined feed line pump 40 and a combined feed linecharge heater 42. In one embodiment, the reactor 16 is a reaction zoneof a single stacked reactor and the reduction zone 18 is a separate zoneof the single stacked reactor. Generally, the hydrocarbon line 20 andthe hydrogen recycle gas line 22 transport hydrocarbons and hydrogengas, respectively, to the combined feed line 26. The combined feed line26 introduces the mixture of hydrocarbons and hydrogen gas into thereactor 16. In the reactor 16, the mixture of hydrocarbons and hydrogengas flows over a catalyst bed, where the actual hydrocarbondehydrogenation reaction takes place. The hydrogen reduction gas line 24introduces hydrogen gas into the reduction zone 18, which is positionedupstream from the reactor 16 and houses fresh catalyst. The freshcatalyst is kept in close proximity to the reactor 16 so that once thecatalyst in the reactor 16 is spent or deactivated, the fresh catalystin the reduction zone 18 can replenish the catalyst in the reactor 16through the catalyst transfer lines 30. When the reduction zone isintegrated above the reactor, the fresh catalyst also serves as acatalyst seal to prevent by-passing of the hydrocarbons and hydrogen gasaround the catalyst bed.

Hydrocarbons are fed into the hydrocarbon dehydrogenation system reactorsection 10 from the combined feed line pump 40 through the hydrocarbonline 20, which transports the hydrocarbons to the combined feed line 26.Hydrogen gas produced in the dehydrogenation process is recycled backinto the hydrocarbon dehydrogenation system reactor section 10 using arecycle gas compressor 14 and is compressed through the hydrogen recyclegas line 22 and into the combined feed line 26, where it is combinedwith the hydrocarbons from the hydrocarbon line 20. Prior to combiningwith the hydrocarbon line 20, the flow rate of the hydrogen gas in thehydrogen recycle gas line 22 can be adjusted such that it combines withthe hydrocarbon in the combined feed line 26 at a predetermined ratio.The ratio will depend on the reaction taking place in the reactor 16.For a hydrocarbon dehydrogenation reaction, the hydrogen to hydrocarbonmole ratio is between about 0.1:1 and about 40:1, and particularlybetween about 3:1 and about 10:1. The flow rate of the hydrogen gas maybe adjusted by any means known in the art. In one embodiment, the flowrate of the hydrogen gas into the combined feed line 26 is adjusted bychanging the motor speed of a screw type recycle gas compressor 14. Thehydrogen gas used in the hydrocarbon dehydrogenation system reactorsection 10 may be wet recycled hydrogen separated from the effluentproduced in the reactor 16. Although the hydrocarbon dehydrogenationsystem reactor section 10 is discussed as using hydrogen gas, othermaterials may be used, such as steam, methane, ethane, carbon dioxide,nitrogen, argon or mixtures thereof.

After the hydrocarbons and the hydrogen gas have combined in thecombined feed line 26, the mixture is sent through the combined feedline heat exchanger 34 and combined feed line charge heater 42 beforebeing introduced into the reactor 16. The combined feed line chargeheater 42 heats the hydrocarbons and hydrogen gas to a temperaturesubstantially similar to the temperature in the reactor 16. In oneembodiment, the combined stream of hydrocarbon and hydrogen gas isheated to a temperature of between about 400° C. and about 600° C.

In the reactor 16, the hydrocarbons and hydrogen gas are passed over acatalyst bed, which decreases the amount of energy required for thehydrocarbon dehydrogenation reaction to occur. In one embodiment, thecatalyst is a layered catalyst composition having an inner core and anouter layer. The inner core is composed of a material which has asubstantially lower adsorptive capacity for catalytic metal precursorsrelative to the outer layer. Examples of the inner core materialinclude, but are not limited to: refractory inorganic oxides, siliconcarbide and metals. The outer layer is bonded to the inner core and iscomposed of an outer refractory inorganic oxide. The outer layer hasuniformly dispersed thereon a platinum group metal, a promoter metal anda modifier metal. The platinum group metals include platinum, palladium,rhodium, iridium, ruthenium and osium. Examples of promoter metalsinclude, but are not limited to: tin, germanium, rhenium, gallium,bismuth, lead, indium, cerium, zinc and mixtures thereof. Modifiermetals include, but are not limited to: alkali metals, alkaline earthmetals and mixtures thereof. Examples of alkali and alkaline earthmetals include, but are not limited to: lithium, sodium, potassium,cesium, rubidium, beryllium, magnesium, calcium, strontium and barium.In a particular embodiment, the catalyst is a platinum/tin-basedcatalyst. Additional information about the catalyst can be found, forexample, in U.S. Pat. Nos. 6,177,381 and 6,280,608, which are hereinincorporated by reference.

Hydrocarbon dehydrogenation conditions include a temperature of fromabout 400° C. to about 600° C., a pressure of from about 1 to about 1013kPa and a liquid hourly space velocity (LHSV) of from about 0.1 to about100 hr⁻¹. As used herein, the abbreviation “LHSV” means liquid hourlyspace velocity, which is defined as the volumetric standard flow rate ofliquid per hour divided by catalyst volume, where the liquid volume andthe catalyst volume are in the same volumetric units. Generally, fornormal paraffins, the lower the molecular weight, the higher thetemperature required for comparable conversion. The pressure in thedehydrogenation zone in the reactor 16 is maintained as low aspracticable to avoid side unselective reactions such as hydrocarboncracking.

After the hydrocarbon dehydrogenation reaction has taken place, theeffluent flows from the reactor 16 through the reactor effluent line 32.The effluent from the reactor 16 generally contains unconverteddehydrogenatable hydrocarbons, hydrogen and products of the hydrocarbondehydrogenation reaction. The effluent is typically cooled and passed toa hydrogen separation zone which typically includes a separator orcontact condenser located downstream of the hydrocarbon dehydrogenationsystem reactor section 10 to separate the hydrogen-rich vapor phase fromthe hydrocarbon-rich liquid phase. Generally, the hydrocarbon-richliquid phase is further separated by means of either a suitableselective adsorbent for the recovery of olefins or a selective reactionor reactions with the desired reaction product recovered by means of asuitable fractionation scheme. Unconverted dehydrogenatable hydrocarbonsare recovered and may be recycled to the reactor 16. Products of thehydrocarbon dehydrogenation reaction are recovered as final products oras intermediate products in the preparation of other compounds.

The hydrogen reduction gas line 24 branches off from the hydrogenrecycle gas line 22 and transports hydrogen gas to the reduction zone18. The reduction zone 18 is positioned upstream of the reactor 16 andhouses fresh catalyst until the catalyst is needed in the reactor 16.Hydrogen gas is passed through the reduction zone 18 so that thecatalyst being housed in the reduction zone 18 is not stored understagnant conditions. By passing hydrogen gas through the reduction zone18, the catalyst is exposed to flowing gas and remains in reduced form.

The hydrogen gas flowing through the hydrocarbon dehydrogenation systemreactor section 10 will usually include some amount of water. Oneexample for a source of water into the hydrocarbon dehydrogenationsystem reactor section 10 includes injecting water into the combinedfeed line 26. In one embodiment, the hydrogen gas has a moisture contentof up to about 6000 parts per million in gas volume (ppmv) water. Asshown and described in further detail below in the Examples section,when hydrogen gas having a moisture content of about 6000 ppmv contactsthe catalyst for an extended period of time, the stability of thecatalyst decreases. The stability of the catalyst decreases when thehydrogen gas passes through the reduction zone 18 and contacts thecatalyst because wet reduction of the catalyst takes place as a resultof exposure to the water in the hydrogen gas, slowly changing ordeactivating the catalyst over time. Therefore, when the catalyst ishoused in the reduction zone 18 for extended periods of time, thecatalyst can begin to change or deactivate before it is even used. Thechange or deactivation of the catalyst in the reduction zone 18 isunexpected because the temperature in the reduction zone 18 is typicallymuch lower than the temperature in the reactor 16 or the temperature atwhich the catalyst is typically pre-reduced in the manufacturingprocess. In a hydrocarbon dehydrogenation process, hydrogen gas istypically passed through the reduction zone 18 at about 20 pounds persquare inch (psi) at a temperature of between about 270° C. and about310° C. Because catalysts used in the hydrocarbon dehydrogenation systemreactor section 10 are typically reduced at about 500° C., it isunexpected that the catalyst would experience any change at such a lowtemperature and low amount of moisture.

To prevent or decrease the amount of wet reduction taking place in thereduction zone 18, the hydrocarbon dehydrogenation system reactorsection 10 includes the catalyst stability system 12. The catalyststability system 12 functions to control the moisture content andtemperature of the hydrogen gas entering the reduction zone 18. It isbelieved that wet reduction of the catalyst is related to the moisturecontent and the temperature of the hydrogen gas and that the moisturecontent and the temperature of the hydrogen gas are inter-related. Thus,a decrease in one of the parameters may allow for an increase in theother parameter without causing wet reduction of the catalyst to takeplace. By maintaining the moisture content and temperature of thehydrogen gas at predetermined levels, catalyst deactivation may beprevented or at least minimized.

The catalyst stability system 12 generally includes a hydrogen gas heatexchanger 36 and a drier 38 positioned upstream of the reduction zone18. The hydrogen gas in the hydrogen reduction gas line 24 is sentthrough the hydrogen gas heat exchanger 36 to heat the hydrogen gas. Inone embodiment, the hydrogen gas in the hydrogen reduction gas line 24is heated to a temperature of between about 100° C. and about 290° C.The drier 38 is positioned at the hydrogen reduction gas line 24downstream from the hydrogen gas heat exchanger 36 and reduces theamount of moisture in the hydrogen gas before it enters the reductionzone 18.

In one embodiment, the hydrogen gas is heated to a temperature ofbetween about 180° C. and about 250° C. and more particularly betweenabout 200° C. and about 220° C. After the hydrogen gas passes throughthe drier 38, the hydrogen gas has a moisture content of less than about6000 parts per million (ppmv). Particularly, the hydrogen gas has amoisture content of between about 3000 ppmv and about 6000 ppmv and moreparticularly between about 3500 ppmv and about 4500 ppmv. Thus, by thetime the hydrogen gas in the hydrogen reduction gas line 24 enters thereduction zone 18, the hydrogen gas has a moisture content of less thanabout 6000 ppmv and a temperature of less than about 250° C. When thehydrogen gas entering the reduction zone 18 has a moisture content ofabout 4000 ppmv and a temperature of about 200° C., the catalyst housedin the reduction zone 18 has a total stability of about 157.5 hours.

In another embodiment, the hydrogen gas is heated to a temperature ofbetween about 250° C. and about 350° C. and more particularly betweenabout 270° C. and about 310° C. After the hydrogen gas passes throughthe drier 38, the hydrogen gas has a moisture content of less than about650 parts per million (ppmv). Particularly, the hydrogen gas has amoisture content of less than about 100 ppmv and more particularly lessthan about 10 ppmv. Thus, by the time the hydrogen gas in the hydrogenreduction gas line 24 enters the reduction zone 18, the hydrogen gas hasa moisture content of less than about 650 ppmv and a temperature ofabove about 250° C. When the hydrogen gas entering the reduction zone 18has a moisture content of about 620 ppmv and a temperature of about 290°C., the catalyst housed in the reduction zone 18 has a total stabilityof about 155 hours.

In another embodiment, the hydrogen gas is heated to a temperature ofbetween about 180° C. and about 250° C. and more particularly betweenabout 180° C. and about 220° C. After the hydrogen gas passes throughthe drier 38, the hydrogen gas has a moisture content of less than about650 parts per million by volume (ppmv). Particularly, the hydrogen gashas a moisture content of less than about 100 ppmv and more particularlyless than about 10 ppmv. Thus, by the time the hydrogen gas in thehydrogen reduction gas line 24 enters the reduction zone 18, thehydrogen gas has a moisture content of less than about 650 ppmv and atemperature of less than about 250° C. When the hydrogen gas enteringthe reduction zone 18 has a moisture content of about 620 ppmv and atemperature of about 200° C., the catalyst housed in the reduction zone18 has a total stability of about 112 hours.

Although FIG. 1A depicts the drier 38 as being positioned on thehydrogen reduction gas line 24 downstream of the hydrogen gas heatexchanger 36 and upstream of the reduction zone 18, the drier 38 may bepositioned anywhere upstream of the reduction zone 18. For example, asshown in FIG. 1B, the drier 38 may also be positioned at the hydrogenrecycle gas line 22 to dry all of the hydrogen gas entering thehydrocarbon dehydrogenation system reactor section 10. Although FIGS. 1Aand 1B depict using a drier 38 to lower the moisture content of thehydrogen gas entering the hydrocarbon dehydrogenation system reactorsection 10, the catalyst stability system 12 may include any piece(s) ofequipment that will reduce the amount of moisture in the hydrogen gasbefore entering the reduction zone 18 without departing from theintended scope of the present invention.

When fresh catalyst is needed in the reactor 16, catalyst flows from thereduction zone 18 through the catalyst transfer line 30 to the reactor16. When catalyst flows to the reactor 16, some amount of hydrogen gasalso flows to the reactor 16. In one embodiment where the reduction zone18 is integrated above the reactor 16 with no isolation in the catalysttransfer line 30, between about 2% and about 10% hydrogen gas constantlyflows from the reduction zone 18 through the catalyst transfer line 30to the reactor 16 to prevent hydrocarbons and hydrogen from the reactor16 entering into the reduction zone 18. The remainder of the hydrogengas in the reduction zone 18 is purged through the reduction gas ventline 28 to avoid stagnant conditions in the reduction zone 18.

FIG. 2 shows a schematic view of a third embodiment of a hydrocarbondehydrogenation system reactor section 100. The hydrocarbondehydrogenation system reactor section 100 includes a catalyst stabilitysystem 102, a recycle gas compressor 104, a reactor 106, a reductionzone or hopper 108, a hydrocarbon line 110, a hydrogen recycle gas line112, a combined feed line 114, a reduction gas vent line 116, a catalysttransfer line 118, a reactor effluent line 120, a combined feed lineheat exchanger 122, a combined feed line pump 140 and combined feed linecharge heater 142. The recycle gas compressor 104, reactor 106,reduction zone 108, hydrocarbon line 110, hydrogen recycle gas line 112,combined feed line 114, reduction gas vent line 116, catalyst transferline 118, reactor effluent line 120, combined feed line exchanger 122and combined feed line charge heater 142 of the hydrocarbondehydrogenation system reactor section 100 are connected and functionsimilarly to the recycle gas compressor 14, reactor 16, reduction zone18, hydrocarbon line 20, hydrogen recycle gas line 22, combined feedline 26, reduction gas vent line 28, catalyst transfer line 30, reactoreffluent line 32, combined feed line exchanger 34 and combined feed linecharge heater 42 of the hydrocarbon dehydrogenation system reactorsection 10 illustrated in FIG. 1A. The hydrocarbon dehydrogenationsystem reactor section 100 differs from the hydrocarbon dehydrogenationsystem reactor section 10 primarily because of the catalyst stabilitysystem reactor section 102 of the hydrocarbon dehydrogenation systemreactor section 100.

The catalyst stability system 102 includes a dry hydrogen gas line 124,a dry hydrogen heat exchanger 126, an inlet flow control valve 128 and acatalyst transfer line isolation valve 132 (catalyst transfer lineisolation valve 132 is part of the catalyst stability system 102 eventhough shown outside the dotted lines). The dry hydrogen heat exchanger126 functions similarly to the hydrogen gas heat exchanger 36 of thecatalyst stability system 12 (FIGS. 1A and 1B) to heat the dry hydrogengas in the dry hydrogen gas line 124. In one embodiment, the hydrogengas is heated to a temperature of less than about 350° C. The inlet flowcontrol valve 128 is connected on the dry hydrogen gas line 124 upstreamof the reduction zone 108 and controls the flow rate of dry hydrogen gasentering the catalyst stability system 102. The dry hydrogen is providedfrom an outside source and is used to keep the catalyst in the reductionzone 108 dry and also for proof reduction of the catalyst. The dryhydrogen gas contains substantially no water and is introduced into thereduction zone 108 to ensure that the catalyst in the reduction zone 108is heated above about 200° C. and more particularly between 270° C. and300° C. prior to transferring catalyst to the reactor 106 to preventthermal shock to the internals of the reactor 106 and for proofreduction of the catalyst. In addition to maintaining a flow through thereduction zone 108, the dry hydrogen gas also maintains the moisturecontent of the reduction zone 108 at a predetermined level. In oneembodiment, the dry hydrogen gas has a moisture content of less thanabout 6000 ppmv. An example of a dry hydrogen source is a pressure swingadsorption (PSA) hydrogen unit. The majority of the hydrogen gasinjected into the hydrocarbon dehydrogenation system reactor section 100should pass through the reduction zone 108 and can be combined with thehydrogen produced from the hydrocarbon dehydrogenation reaction into thehydrogen supply system.

The dry hydrogen gas flowing through the reduction zone 108 is purgedfrom the reduction zone 108 at the reduction gas vent line 116 to avoidstagnant conditions. The catalyst transfer line isolation valve 132 isconnected in the catalyst transfer line 118 between the outlet of thereduction zone 108 and the inlet of the reactor 106. The catalysttransfer line isolation valve 132 controls the flow of catalyst from thereduction zone 108 to the reactor 106 and is switchable between an openposition and a closed position. Generally, the catalyst transfer lineisolation valve 132 is in the closed position and maintains the catalystin the reduction zone 108. When catalyst is needed in the reactor 106,the catalyst transfer line isolation valve 132 opens and fresh catalystis allowed to flow from the reduction zone 108 to the reactor 106through the catalyst transfer line 118. In one embodiment, the catalysttransfer line isolation valve 132 is a double block and bleed valve thatprovides positive isolation between the reduction zone 108 and thereactor 106 to prevent catalyst, air or hydrogen gas fromunintentionally entering the reactor.

FIG. 3 shows a schematic view of a fourth embodiment of a hydrocarbondehydrogenation system reactor section 200. The hydrocarbondehydrogenation system reactor section 200 includes a catalyst stabilitysystem 202, recycle gas compressor 204, a reactor 206, a reduction zoneor hopper 208, a hydrocarbon line 210, a hydrogen recycle gas line 212,a hydrogen reduction gas line 214, a combined feed line 216, a reductiongas vent line 218, a catalyst transfer line 219, a reactor effluent line220, a combined feed line heat exchanger 222, a combined feed pump 240and a combined feed line charge heater 242. The recycle gas compressor204, reactor 206, reduction zone 208, hydrocarbon line 210, hydrogenrecycle gas line 212, hydrogen reduction gas line 214, combined feedline 216, reduction gas vent line 218, catalyst transfer line 219,reactor effluent line 220, combined feed line heat exchanger 222,combined feed pump 240 and combined feed line charge heater 242 of thehydrocarbon dehydrogenation system reactor section 200 are connected andfunction similarly to the recycle gas compressor 14, reactor 16,reduction zone 18, hydrocarbon line 20, hydrogen recycle gas line 22,hydrogen reduction gas line 24, combined feed line 26, reduction gasvent line 28, catalyst transfer line 30, reactor effluent line 32,combined feed line heat exchanger 34, combined feed pump 40 and combinedfeed line charge heater 42 of the hydrocarbon dehydrogenation systemreactor section 10 illustrated in FIG. 1A. The hydrocarbondehydrogenation system reactor section 200 differs from the hydrocarbondehydrogenation system reactor section 10 primarily because of thecatalyst stability system 202 of the hydrocarbon dehydrogenation systemreactor section 200.

The catalyst stability system 202 includes an inert gas line 224, aninert gas inlet valve 226, a hydrogen gas inlet valve 228, an inert gasoutlet isolation valve 230, a catalyst transfer line isolation valve232, an inert gas heat exchanger 234 and a reduction gas vent lineisolation valve 244 (inert gas outlet isolation valve 230, catalysttransfer line isolation valve 232 and reduction gas vent line isolationvalve 244 are part of the catalyst stability system 202 even thoughshown outside the dotted lines). The inert gas heat exchanger 234functions similarly to the gas heat exchanger 34 of the catalyststability system 12 (FIGS. 1A and 1B) to heat the inert gas in the inertgas line 224. In one embodiment, the inert gas is heated to atemperature of less than about 350° C. The inert gas inlet valve 226 isconnected on the inert gas line 224 upstream of the reduction zone 208and controls the flow rate of inert gas entering the catalyst stabilitysystem 202. The inert gas outlet isolation valve 230, the reduction gasvent line isolation valve 244 and catalyst transfer line isolation valve232 are switchable between open and closed position. In one embodiment,both the inert gas outlet isolation valve 230 and reduction gas ventline isolation valve 244 are configured as double block and bleedsystems to prevent hydrogen from mixing with the inert gas system andinert gas from mixing with the hydrogen supply system. Generally, thecatalyst transfer line isolation valve 232 will be closed unlesstransferring fresh catalyst from the reduction zone 208 into the reactor206. While purging the reduction zone 208 with inert gas, the inert gasoutlet isolation valve 230 is open and the reduction gas vent lineisolation valve 244 is closed to prevent any inert gas from leavingthrough the reduction gas vent line 218. The inert gas containssubstantially no water and is introduced into the reduction zone 208 toensure that the catalyst in the reduction zone 208 does not becomestagnant. In addition to maintaining a flow through the reduction zone208, the inert gas also maintains the moisture content of the reductionzone 208 at a predetermined level. In one embodiment, the inert gas hasa moisture content of less than about 6000 ppmv. The inert gas may beany gas that does not react with the catalyst housed in the reductionzone 208. In one embodiment, the inert gas is nitrogen.

In the hydrocarbon dehydrogenation system reactor section 200, thehydrogen reduction gas line 214 is re-routed to feed the hydrogen gasinto the inert gas line 224 downstream of the inert gas inlet valve 226and upstream of the inert gas heat exchanger 234. The hydrogen gas inletvalve 228 and inert gas inlet valve 226 are switchable between open andclosed positions. In one embodiment, both the hydrogen gas inlet valve228 and inert gas inlet valve 226 are configured as double block andbleed systems to prevent hydrogen from mixing with the inert gas systemand inert gas from mixing with the hydrogen supply system. The hydrogengas inlet valve 228 controls the amount of hydrogen gas that enters theinert gas line 224. In one embodiment, the volume of nitrogen in thereduction zone 208 is considered negligible and is allowed to be purgedinto the hydrogen supply system. When switching to hydrogen gas flow,the inert gas outlet isolation valve 230 will close and the reductiongas vent line isolation valve 244 will open allowing both the retentionvolume of nitrogen in the reduction zone 208 and the hydrogen gas toleave through the reduction gas vent line 218. The inert gas inlet valve226 will be closed. The hydrogen gas functions to proof-reduce thecatalyst and to purge the reduction zone 208 and the catalyst transferline 219 for a short period of time to remove any inert gas beforeallowing catalyst to flow from the reduction zone 208 to the reactor206. Thus, even if the hydrogen gas stream is wet, the moisture willhave a minimal effect on the catalyst. Before entering the catalysttransfer lines 219, the hydrogen gas flowing through the hydrogenreduction gas line 214 is heated in the inert gas heat exchanger 234.

When catalyst is needed in the reactor 206, the flow of hydrogen gas ismaintained and the catalyst transfer line isolation valve 232 opens andcontrols the rate of catalyst flowing from the reduction zone 208 andinto the reactor 206. When the catalyst transfer isolation valve 232 isin the open position, fresh catalyst is allowed to flow from thereduction zone 208 to the reactor 206 through the catalyst transfer line219. In one embodiment, the catalyst transfer isolation valve 232 is adouble block and bleed valve that prevents catalyst or inert gas fromunintentionally entering the reactor 206.

EXAMPLES

The present invention is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present inventionwill be apparent to those skilled in the art. Unless otherwise noted,all parts, percentages, and ratios reported in the following examplesare on a weight basis, and all reagents used in the examples wereobtained, or are available, from the chemical suppliers described below,or may be synthesized by conventional techniques.

Catalyst Pre-Treatment

Two catalysts typically used in hydrocarbon dehydrogenation processes,DeH-15 and DeH-11, both available form UOP, Des Plaines, Ill., weretested to determine their stability and methyl cyclohexane (MCH)conversion ability at varying conditions. About 430 cubic centimeters(cc) of the catalyst was loaded into an isoterm zone of a stainlesssteel reactor. The space above and below the catalyst bed was packedwith inert spacer. The treatment gas mixture contained about 160.84 L/hof hydrogen gas and about 620 parts per million by volume (ppmv) H₂O.The moisture level was obtained by injecting about 0.1 cc/h of waterinto the hydrogen gas line using an ISCO pump. An injection of water wasintroduced at the start of ramp. The reactor temperature was raised tothe target temperature (either 200° C. or 290° C.) at a ramp rate ofabout 1.5° C./min. Once the reactor reached the target temperature, thereactor was kept at the target temperature for about 116 hours whilemaintaining the gas mixture composition and flow rate. After about 116hours, water injection was cut off and the reactor was cooled down withhydrogen gas to room temperature. Nitrogen gas was used to briefly purgethe reactor before unloading.

DeH-15 was used as the catalyst in Examples 1, 2, 3, 4 and 5 andComparative Examples A, B and C. DeH-11 was used as the catalyst inExamples 6, 7, 8, 9 and 10 Comparative Examples D and E. The catalystswere either tested fresh (Comparative Examples A, C and D) or afterbeing pre-treated (Examples 1-10 and Comparative Examples B and E) witha gas stream.

The catalysts used in Examples 1 and 2 were pre-treated with a gasstream having properties designed to simulate reduction zone conditionsfor a hydrocarbon dehydrogenation process of the present invention.

The DeH-15 catalyst used in Comparative Examples A and C were fresh andwas not subject to any pre-treatment. The DeH-15 catalyst used inComparative Example B was pre-treated with a gas stream havingproperties designed to simulate reduction zone conditions for aconventional hydrocarbon dehydrogenation process.

Similarly, the DeH-11 catalyst used in Comparative Example D was freshand was not subject to any pre-treatment while the DeH-11 catalyst usedin Comparative Example E was pre-treated with a gas stream havingproperties designed to simulate reduction zone conditions for aconventional hydrocarbon dehydrogenation process.

Table 1 lists the parameters of the gas used to pre-treat the catalystsof each of Examples 1-10 and Comparative Examples A-E.

Temp. Water Content Duration Gas Outlet Catalyst Condition Gas (° C.)(ppmv) (h) Pressure (psi) Example 1 DeH-15 Pre-treated H₂ 290 620 116 20Example 2 DeH-15 Pre-treated H₂ 200 4000 116 20 Example 3 DeH-15Pre-treated H₂ 200 620 116 20 Comp. DeH-15 Fresh None None None NoneNone Example A Comp. DeH-15 Pre-treated H₂ 290 4000 116 20 Example BExample 4 DeH-15 Pre-treated N₂ 200 4000 116 20 Example 5 DeH-15Pre-treated N₂ 200 620 116 20 Comp. DeH-15 Fresh None None None NoneNone Example C Example 6 DeH-11 Pre-treated H₂ 290 620 116 20 Example 7DeH-11 Pre-treated H₂ 200 4000 116 20 Example 8 DeH-11 Pre-treated H₂200 620 116 20 Comp. DeH-11 Fresh None None None None None Example DComp. DeH-11 Pre-treated H₂ 290 4000 116 20 Example E Example 9 DeH-11Pre-treated N₂ 200 4000 116 20 Example 10 DeH-11 Pre-treated N₂ 200 620116 20Stability Test

To determine catalyst stability, various catalysts were tested in alaboratory scale plant. The catalysts were placed in a reactor and thetemperature of the reactor was raised to about 479.4° C. (895° F.) inhydrogen gas before a hydrocarbon feed was introduced. A hydrocarbonfeed composed of about between about 12 wt % and about 13 wt % of n-C₁₀,between about 28 wt % and about 29 wt % of n-C₁₁, between about 29 wt %and about 30 wt % of n-C₁₂, between about 27 wt % and about 28 wt % ofn-C₁₃, up to about 1 wt % of n-C₁₄ and between about 1 wt % and about1.5 wt % of non-normals was allowed to flow over the catalyst under anoutlet pressure of about 20 pounds per square inch (psig) at a hydrogengas stream and hydrocarbon stream ratio of about 4:1. The liquid hourlyspace velocity (LHSV) was at about 28 hr⁻¹. Hydrogen gas and hydrocarbonfeed were combined upstream of the reactor to form a combined feed whichwas vaporized prior to entering the reactor. The total normal olefinconcentration in the product (% TNO) was maintained at about 16.9±1 wt %during the stability test by adjusting the reactor inlet temperature.

The product was analyzed hourly by online gas chromatography to quantifythe normal olefin yield. At the start of the run (SOR), no water wasinjected. The concentration of water in the combined feed was less thanabout 10 wt-ppm based on the weight of the combined feed. As thecatalyst started to deactivate, the temperature was increased tomaintain the same TNO of about 16.9. Once the reactor temperature at 3inches above the catalyst bed reached about 493.3° C. (920° F.), thecatalyst was regarded as deactivated and the run was stopped. Thistested the dry mode stability of the catalyst.

To test the water management mode stability of the catalysts, an extrastep was added after the reactor temperature reached about 493.3° C. inthe dry phase. About 2000 ppmv of water was then injected into thereactor to combine with the hydrogen gas and hydrocarbon feed andvaporized prior to entering the reactor. The reactor temperature wasalso decreased to about 479.4° F. to maintain the TNO at about 16.9. Theend of run (EOR) was determined as when the reactor temperature reachedabout 493.3° C. again. The time between the SOR and EOR was used tocompare catalyst stability. When the reactor temperature reached about493.3° C., the feed and water injection were stopped and the reactor wascooled down under the flow of hydrogen gas.

Table 2 shows the stability of the catalysts treated in Examples 1-10and Comparative Examples A-E. The stability of the catalysts weremeasured by the number of hours the catalyst remained active. Once thereactor temperature reached about 493.3° C. to achieve a TNO of about16.9, the catalyst was no longer considered to have enough activity tobe used effectively.

TABLE 2 Stability in Dry phase (h) Total Stability in WM (h) Example 188 155 Example 2 93 157.5 Example 3 60 112 Comp. Example A 95 164 Comp.Example B 48 100 Example 4 81 148 Example 5 71 135 Comp. Example C 93158 Example 6 87 120 Example 7 90 122 Example 8 83 116 Comp. Example D98 145 Comp. Example E 72 112 Example 9 70 112 Example 10 88 115

As illustrated in Table 2, the fresh catalysts used in ComparativeExamples A, C and D were stable for the longest amounts of time. Bycontrast, at conditions simulating a reduction zone in a conventionalhydrocarbon dehydrogenation process (Comparative Examples B and E), thestability of the catalyst decreased substantially. In particular, thedry mode life of the DeH-15 catalyst pre-treated with hydrogen gas(Comparative Example B) decreased by almost 50% from about 95 hours toabout 48 hours while the life of the DeH-11 catalyst (ComparativeExample E) pre-treated with hydrogen gas decreased by about 26.7%, fromabout 98 hours to about 72 hours. Similar results were shown in thewater management mode, with the life of the DeH-15 catalyst decreasingby about 39% and the life of the DeH-11 catalyst decreasing by about22.8%. Because the stability of the DeH-11 catalyst decreased to alesser extent than the DeH-15 catalyst, Comparative Examples A and B andComparative Examples D and E illustrate that the DeH-11 catalyst isaffected by the temperature and moisture content of the gas stream to alesser degree than the DeH-15 catalyst.

When only the moisture content of the gas stream was decreased to about620 ppm and the temperature remained at about 290° C. (Examples 1 and6), the life of the catalysts decreased only slightly compared to thelife of fresh catalyst. In particular, the dry mode life of the DeH-15catalyst pre-treated with hydrogen gas (Example 1) decreased by onlyabout 7.37% and the dry mode life of DeH-11 catalyst pre-treated withhydrogen gas (Example 6) decreased by only about 11.2%. Similar resultswere shown in the water management mode, with the life of the DeH-15catalyst decreasing by only about 5.49% and the life of the DeH-11catalyst decreasing by only about 17.24%. Examples 1 and 6 illustratethat lowering only the moisture content of the gas stream will increasethe lifetime of the DeH-15 and DeH-11 catalysts compared to the lifetimeof DeH-15 and DeH-11 catalysts exposed to conventional dehydrogenationprocess conditions.

When only the temperature of the gas stream was decreased to about 200°C. and the moisture content remained at 4000 ppm (Examples 2, 4, 7 and9), the life of the catalysts decreased only slightly compared to thelife of fresh catalyst. In particular, the dry mode life of the DeH-15catalyst pre-treated with hydrogen gas (Example 2) decreased by onlyabout 2%, the dry mode life of DeH-15 catalyst pre-treated with nitrogengas (Example 4) decreased by only about 13%, the dry mode life of DeH-11catalyst pre-treated with hydrogen gas (Example 7) decreased by onlyabout 8% and the dry mode life of DeH-11 catalyst pre-treated withnitrogen gas (Example 9) decreased by only about 2.78%. Similar resultswere shown in the water management mode. Examples 2, 4, 7 and 9illustrate that lowering only the temperature of the gas stream willincrease the lifetime of the DeH-15 and DeH-11 catalysts compared to thelifetime of DeH-15 and DeH-11 catalysts exposed to conventionaldehydrogenation process conditions.

Table 2 also illustrates that when the temperature and the moisturecontent of the gas stream were both decreased from the conditions of aconventional hydrocarbon dehydrogenation process, the life of thecatalyst may still decrease, but to a lesser extent. In particular, whenthe hydrogen gas stream had a H₂O content of about 620 ppmv and atemperature of about 200° C. (Example 3), the dry mode life of theDeH-15 catalyst only decreased about 37%, compared to the 50% decreaseexhibited when the hydrogen gas stream had a H₂O content of about 4000ppmv and a temperature of about 290° C. (Comparative Example B). Thus,when a catalyst is housed in a reduction zone for an extended period oftime while being exposed to a gas having a relatively high moisturecontent and at higher temperatures, the catalyst becomes unstable,decreasing the stability of the catalyst. As can also be seen from Table2, this trend holds regardless of the gas used to pre-treat thecatalyst. The stability of the catalyst when either hydrogen gas ornitrogen gas was used decreased relative to the stability of freshcatalyst, but increased relative to the stability of catalyst exposed toa higher moisture content and temperature.

In particular, the catalyst used in Example 5, which was DeH-15 catalystpre-treated with nitrogen gas at 200° C. and a water content of about620 ppm, had a stability of about 71 hours in the dry mode and about 135hours in the water management mode. The catalyst used in Example 3,which also was DeH-15, was exposed to hydrogen gas under the sameconditions and had a dry phase stability of about 60 hours and a watermanagement mode stability of about 112 hours.

Methyl Cyclohexane (MCH) Dehydrogenation Test

To determine the properties of catalysts after being exposed tomoisture, the ability of the catalysts to dehydrogenate methylcyclohexane to toluene was tested. The MCH test is a probe reaction usedto gauge the metal function (e.g., dehydrogenation ability) of thecatalyst. After pretreatment, about 1 cc of catalyst was loaded into theMCH dehydrogenation testing reactor and about 1.0 grams of 40-60 meshsand was also added to fill void spaces between the catalyst. A purgestream of hydrogen gas bypassed the MCH saturator and was used topre-reduce the catalyst before MCH testing. The hydrogen gas flow ratewas about 250 cc/min while the reactor was held at about 200° C. forabout half an hour with about a 6.67° C./min ramp rate and was held atabout 565° C. for about three hours.

The reactor was then allowed to cool down to about 300° C. at a ramprate of about 2.0° C./min and held at about 300° C. Hydrogen gas thenbypassed the reactor but still passed through the MCH saturator. The MCHsaturator was kept at about 0° C. After hydrogen gas flowed through theMCH saturator for about 15 minutes, a mixture of hydrogen gas and MCHwas introduced into the reactor. Once the temperature reached about 300°C. for about 20 minutes, online gas chromatography was used to analyzethe reaction products.

The same procedure was applied when the reactor temperature was raisedfrom about 300° C. to about 325° C., from about 325° C. to about 350°C., from 350° C. to about 375° C., from about 375° C. to about 400° C.,from about 400° C. to about 450° C. and from about 450° C. to about 500°C., respectively, with a ramp rate of about 2.0° C./min. The reactor wasthen cooled down to about room temperature by hydrogen gas (bypassingthe MCH saturator). The percent conversion from MCH to toluene at eachof the temperatures was measured.

Table 3 shows the MCH conversion of the catalysts used in Examples 1-10and Comparative Examples A-E. The amount of MCH conversion is correlatedto the activity of the catalyst.

TABLE 3 MCH Conversion (%) 325° C. 350° C. 375° C. 400° C. 450° C. 500°C. Example 1 0.38 1.07 1.83 3.26 8.95 20.06 Example 2 0.38 0.52 1.062.01 5.74 14.09 Example 3 0.32 0.67 1.73 3.15 8.71 20.36 Comp. 0.33 0.892.27 3.91 11.4 25.97 Example A Comp. 0 0 0.37 1.91 5.43 14.26 Example BExample 4 0.23 0.57 1.18 2.04 6.16 14.77 Example 5 0.21 0.59 1.34 2.607.64 18.19 Comp. 0.39 0.89 1.88 3.48 9.89 22.81 Example C Example 6 0.470.73 1.23 2.15 5.98 15.44 Example 7 0.19 0.48 0.96 1.60 4.50 12.10Example 8 0.15 0.60 1.15 2.26 7.35 19.5 Comp. 0.21 0.62 1.44 2.85 9.0023.85 Example D Comp. 0 0 0.41 2.19 7.16 22.7 Example E Example 9 0.340.52 1.00 1.78 5.46 14.52 Example 10 0.18 0.49 1.15 2.09 6.45 16.98

As can be seen in Table 3, the ability of fresh DeH-15 and DeH-11catalyst (Comparative Examples A, C and D) to convert MCH to tolueneincreased as the temperature of the reactor increased. The ability ofpre-treated catalyst to convert MCH to toluene also increased as thetemperature of the reactor increased. In particular, at about 400° C.,the fresh DeH-15 catalyst of Comparative Example A resulted in almost 4%MCH conversion. By comparison, when the DeH-15 catalyst was exposed toabout 4000 ppmv H₂O at about 290° C. (Comparative Example B), the MCHconversion was about 1.91%, a decrease of about 51.2% compared to freshDeH-15 catalyst. When the DeH-15 catalyst was only exposed to about 620ppmv H₂O at about 200° C. (Example 3), the MCH conversion decreased byonly about 19.4% compared to fresh DeH-15 catalyst, converting about3.15% of the MCH to toluene. Similar trends were found when either thetemperature or the moisture content was varied. When hydrogen gas wasused, the amount of MCH converted to toluene was generally between theamount of MCH converted when the catalyst was not exposed to anypre-treatment and the amount of MCH converted when the catalyst wasexposed to conventional dehydrogenation process conditions. However,when nitrogen gas was used, the amount of MCH converted to toluenedecreased by up to about 25% when compared to the amount of MCHconverted when the catalyst was exposed to fresh catalyst.

The results in Table 3 indicate that the DeH-11 catalyst was moreresilient than the DeH-15 catalyst to moisture content and temperature.While fresh DeH-11 catalyst converted about 2.85% of the MCH to toluene(Comparative Example D), DeH-11 catalyst exposed to about 4000 ppmv H₂Oat about 290° C. (Comparative Example E) converted about 2.19% of theMCH to toluene at about 400° C., a decrease of less than about 23.1%.Similarly, when the DeH-11 catalyst was pretreated with about 620 ppmvH₂O at about 200° C. (Example 8), the MCH conversion decreased by onlyabout 20.7%. Similar trends were found when either the temperature orthe moisture content was varied. The amount of MCH converted to toluenewas either between the amount of MCH converted when the catalyst was notexposed to any pre-treatment and the amount of MCH converted when thecatalyst was exposed to conventional dehydrogenation process conditionsor was substantially similar to the amount of MCH converted when thecatalyst was exposed to conventional dehydrogenation process conditions.

The invention has been described with reference to various specific andpreferred embodiments and techniques. However, it should be understoodthat many variations and modifications may be made while remainingwithin the spirit and scope of the invention.

The invention claimed is:
 1. A method of increasing stability of acatalyst used in a dehydrogenation process, the method comprising:storing fresh catalyst in a storage hopper for an average catalystresidence time between 100 and 200 hours; passing a gas through thestorage hopper, wherein the gas has a moisture content ranging fromabout 600 ppmv to about 4000 ppmv and where the gas is maintained at atemperature between 200° C. and about 290° C., and wherein the gas is anon-oxidizing gas selected from the list consisting of hydrogen,methane, ethane, carbon dioxide, nitrogen, argon and mixtures thereof;introducing hydrocarbons and hydrogen gas into a reactor positioneddownstream from the storage hopper to facilitate a dehydrogenationreaction, wherein the reactor includes catalyst for increasing the rateof the dehydrogenation reaction; and replenishing spent catalyst in thereactor with fresh catalyst from the storage hopper.
 2. The method ofclaim 1, wherein passing the gas through the storage hopper comprisespassing a hydrogen gas stream through the storage hopper.
 3. The methodof claim 2, wherein maintaining the moisture content of the gas fromabout 600 ppmv to about 4000 ppmv comprises passing the gas through adrier positioned upstream of the storage hopper.
 4. The method of claim1, wherein maintaining the moisture content of the gas from about 600ppmv to about 4000 ppmv comprises passing inert gas through the storagehopper.